Telemeter



Jime 15, 1926.

TELEMETER Filed August 13. 1921 4 Sheets-Sheet 1 Fig. 2

June 15 1926.

O. EPPENSTEIN TELEMETER Filed August 13, 1921 4 Sheets-Shag; 5

lll ll June 15, 1926. 1,589,132

0. EPPENSTEIN TELEME'IER Y Filed August 15. 1921' 4 sheets-sheet 4value, so that'any Patented June 15, 1 926.

OTTO EPPENSTEIN, OF JENA, GERMANY, ASSIGlfl'OR,

BY mnsrm ASSIGNMENTS, TO

BAUSCH & LOMB OPTICAL COMPANY, OF ROCHESTER, NEW YORK, CORPORA- TION OFNEW YORK.

TELEHETER.

Application filed August 13, 1921, Serial N'o. 492,107, and in GermanyJuly 21, 1919.

(GRANTED UNDER THE PROVISIONS OF THE ACT OF MARCH 3, 1921, 41 STATSL,13-13.)

The invention relates to telemeters of the well-known, usualconstruction with the baseline in the instrument and having two telescope systems with their objective axes lying if in the base-line, infront of each of which, at the corresponding end of the base-line, areflecting system is disposed, which is nonsensitive to slight rotationsin the plane of measurement, deflects the entering, pencils of rays by90 in the plane of measurement and leads them directly to thecorresponding telescope system. The other component parts of thesetelemeters, such as the separat- 15 the measur ng device etc., are of noimportance as regards the invention and'can be of any desiredconstruction. Every telemeter of this type requires, as is well known,to

have its indicating arrangement corrected from time to time as it isimpossible in practice to keep the se arate component parts of thelatter and t eir relative position entirely invariable. The correctionofsuch telemeters has usually been eflect'ed heretofore with the aid of acorrectin lath or some equivalent means, which ma 'es it possible topresent two marks to the telemeter, which correspond to aninfinitely'distant object, so that after setting the telemeter to thesemarks the indicating device can be caused to read infinity and thetelemeter can be thus corrected. Another known method consists inplacing an auxiliary reflecting system in front of the telemeter, bywhich the base-line of the instrument can betemporarily broughtto thezero object (not too near in practice) must ivethe reading infinity inthe telemeter an a rectification of the indicating device by it ispossible. Thereby, in

thepresent case as well as throughout the following the .base-line ofthe value zpro signifies that the base-line has the value -.zero in thedirection which is essential for measuring. The chief drawback obothmethods is, that the correctinglath or the corresponding. auxiliaryarrangement must always be carried along with the instrument, Further ithas become known through Patent 1,085,- 883, to give thetelemetertemporarily the base-line zero by a suitable change over of thereflecting systems used in the telemeter itself, and then to correct thereading infining prism system, the ocular arrangement,

The total error of reflection,

ity againwith the aid of any distant object, As e'xplalned in the saidpatent, the condition must be fulfilled, that, on the reflecting systemsbeing changed over, the total error of reflection shall not change itsvalue as regards magnitude and sign. The said patent dealshowever,through'out with forms -of telemeters, which deviate from theform defined at thev beginning of this and have mostly a considerablymore complicated ar-- rangement. The object of the invention consists ingiving telemeters of the above mentioned simple form temporarily thebaseline zero without the employment of further auxiliary means usingonly the two reflecting systems alread provided in the telemeter, so asto be a le at any time to carry out a correction with the aid of anydistantobject. For this purpose the two reflecting systems, which arelocated at-the endsof the base-line, are so formed and disposed, whilepreserving the non-sensitiveness to slight rotations in the plane ofmeasurement, that for the correction one of the reflecting systems canbe placed unchanged in front of themtrance opening of the stationarysecond refleeting system and a base-line of the yalue zero is therebybrought about. Thus, after one of the reflecting systems has beenchanged, over into the correcting arrangement, the encils of rays comingfrom any distant ob ect enter directly into one of the telescope systemsin the direction of the original base-line, while they reach the othertelescope system after passing through both reflecting systems,beingthusdeflected twice through in the plane of measurement. which mayhave been present in themeasuring device,

remains the same in the correcting sition as well, as only the possibleerror 0 reflection of the reflecting system. that can be changed over,which was previously effective only on one side, 1s now transferredunaltered as'to magnitude and sign to the other side and is addeddirectly to the error of reflection of the second reflecting system. Asboth telescope objectives lie with their axes in the base-line, a.slight displacement in the vertical direction is required forthe pencilsof rays, which in the correcting position have to pass through bothreflecting systems, in order to transmit, them above or v below thetelescope systems to the other side of the telemeter. This slightdisplacement in the vertical direction, which can be effected by onereflecting system only or by both, partially by each, can of course notbe avoided in the measuring position so that the pencils of rays comingfrom he object to be measured do not enter accurately in the samehorizontal plane into the telemeter, but only pass into the plane ofmeasurement containing the base-line, after passing through thereflecting systems. In practice this slight dislacement in the heightdirection is known to be of little importance.

Reflecting systems having the properties enumerated may be built up invarious ways.

A simple constructional form of the invention is obtained by using areflecting system known of itself, which is composed of two right-angledreflecting prisms, a larger one, in which the two cathetal surfaces actas reflecting surfaces, and a second prism of half the size, in whichthe=hypotenusal surface is used as the reflecting surface. The twoprisms are arranged in the same way as a Porro prism system,'.the lastreflecting surface of which has'been removed,-so that al y by thisamount such a system can be-'termed a three-quarter Porro system.This'lsystem may also be imagined as reflecting surface of'an opticalsquare w1th a deflection of 90 being replaced by a' ridge surface, theaxial ray-= not being allowed to impinge on the ridge itself but beingdisplaced perpendicular to the ridge. Consequently this system has theproperty, just like an optical square, of being non-sensitive to smallrotations in the plane of deflection. Such a reflectin system on oneside of the base-line in com ination with a second reflecting systemlike it or an ordinary optical square on the other side of the base-linemake a number of arrangements possible, which ecorrespond to theinvention. Ordinary optical squares may also be used on both sides ofthe base-line, but in this case, as, when opposing the two opticalsquares, the distance apart of the axial rays corresponding to theirdimensions is retained, a pair of parallel reflectors facing eachothermust be used in addition, which displaces the axial ra corresponding tothe base-line zero laterand at the same time effects the above mentioneddisplacement in the vertical direction. This pair 9f parallel reflectorscan be combined in a suitable mansquares. In the ner w1th one of theoptical case of such an arrangement the number of o -reflecting surfacesis greater by one as comared with the first named constructional orms atleast in one of. the two reflecting s stems. If a still greater numberof recting surfaces be a mitted, if for instance one of the reflectingsurfaces be repla'ced by having been derived from one .uring arrangementa ridge surface, further constructional forms may be derived withoutdifficulty. In ever case it remains fundamentally immateria, which .ofthe two reflecting systems is arranged so as to be changed over. Forpractical reasons as a rule the simpler one will be used for thispurpose. -Similarly it is immaterial as regards the essence of theinvention, whether the reflecting systems be embodied by actualreflectors or combined from reflecting prisms. For the practicalconstruction of a telemeter according to the invention the change-oversystem will be combined with a casing or a mount, for which, both in themeasuring position and in the correcting position, suitable guides andstops are provided on the casing of the telemeter, so that thereflecting system may be conveniently and quickly chan ed over.

The idea of placing one reflecting system in front of the other in atelemeter, provided at both ends of the base-line with three-quarterPorro systems, for correcting purposes, has already been mentioned inthe British Patent 18273 of the year 1902. The possibility of therebyobtaining the base-line zero and of thus beingv able to correct thetelemeter at any time without auxiliary means is however not present inconsequence of the quite different general arrangement. On the contraryit is pomted out that a small base-line still remaining after thechangeover can only be brought to the value zero, by employing specialauxiliary means, name ly a rhombic reflecting prism. This rhombic prismon its part also suffers from a reflecting error, which must be takeninto account and therefore requires an adjustment in two differentpositions, so that a considerably more complicated method of correctionresults than with the telemeter according to the invention.

In the annexed drawing the invention is illustrated by a number ofdifferent constructional forms in a diagrammatic manner. Eachconstructional form is shown by an elevation and a plan view drawn belowit. Figs. 1 and 2 show 3 and 4 the second example, the third example,Figs. 7 and 8 the fourth example, Figs. 9 and 10 the fifth example,

the first example. Figs. Figs. 5 and 6' which is Figs. 11 -to 13 thesixth example, Figs. 14:

to 16 the seventh example. The parts of the telemeter that areof no imortance for the invention are uniformly indicated in all the examples,the two telescope objectives lying with their axes in the base-line bytwo lenses a, and (1 the separating prism system by two crossedreflectors b and b the ocular system by a lens 0 and the measby arefracting prism d, which is dis laceable in the direction of the baseline. 6f the two reflecting systems at the ends of the base-line theleft hand one is always assumed to be the stationary one 1. e. thecorrecting position. Of course in every case the two reflecting systemsmay change place.

Figs. 1 and 2 show a telemeter, which has as stationary reflectingsystem a three-quarter Porro system. e and as change over system apentagonal prism e The Porro system e which displaces the pencils ofrays entering on the left hand side of the telemeter downwardly by asmall amount, is so disposed that the pentagonal prism e after arotation of 180 in the plane of measurement, can be brought simply infront of the entrance aperture of the orro system 6 v and the base-linezero thus produced. For

this purpose the parts of the telemeter, serving the entrance of therays, are constructed in the following manner. The two ends of a tubularcasing m, carrying the telescope systems are carried out as prism headswhich are denoted by n and 12 The prism head a is closed on the sidefacing the observer by a lid 0 and contains the three-quarter Porrosystem e whose position is secured by gripping jaws p and p and screwsand The prism head n is provided with an aperture 12?, which lies in theoptical telescope axis and through which the light enters the telescopeobjective-a during the correcting process. It comprises a prism casing 1containing the pentagonal prism e and closed by a lid 1' which casing isfixed by fine screws s .9 s, s and 8 After loosening these screws theprism casing r can be drawn out from the prism head 91? and insertedinto the prism head 72., having a corresponding opening n, in thepositlon required for the correction. The prism e is fixed in the prismcasing 'rbya screw it by means of a gripping jaw u, '0' fixed on the lid1' In the example shown in Figs. 3 and 4 inversely the stationaryreflecting system is embodied by a pentagonal prism f and the changeover reflecting system by a threequarter Porro system f For bringing thechange-over reflecting system f into the corrooting position in thiscase a rotation in the base-line through 180 is first necessary andthereupon a rotation in the plane of measurement through 90".

I The telemeter shown in- Figs. 5 and 6 has at both ends of thebase-linethree- ,quarter Porro systems a and 9 respectively, these twosystems being exactly similar, so that the entering pencils of rays aredisplaced downwards on' one side and upwards on the other side by thesame amount.

For producing the correcting arrangement.

the same alteration in positionsof'the right hand reflecting system 9 isrequired as in the example according to Figs. 3 and 4.

and by a spring- In the constructional form shown by Figs. 7 and 8 twoPorro systems h and 71, which are symmetrical to the Porro system of theformer example, are used, the right hand reflecting system 72. beingsomewhat differently arranged so that for bringing about the correctingposition only a rotation through 180 in the plane of measurement isrequired.

The arrangement according to Figs. 9 and 10 also has two three-quarterPorro systems, two slightly different forms however, viz on the righthand side the system 5 which is symmetrical to the Porro system of theexample Figs. 5 and 6, on the left hand side on the other hand a Porrosystem i with a displacement of the pencils of rays in the verticaldirection, which is twice as great and equally directed. Thereby, as isseen from the figures, the total displacement of the entering pencils ofrays relatively to each other may be reduced bothin the measuringposition and in the correcting position to half the amount of the twoformer examples. In this case as well for the correcting position thesame alteration of'position of the change-over system i is to beeffected as in the example according to Figs. 5 and 6.

Figs. 11 and 12 show a constructional example, in which on both sides ofthe baseline. optical squares in the form of pentagonal prisms k and kare used, the changeover prism b however being firmly cemented to arhombic prism k, which brings about the requisite displacement of thecorrecting position, the right hand refleeting system H, is must berotated through 180 in the plane of measurement.

The last constructional example, Figs. 14 to 16, alsohas optical squaresat both ends of the base-line, the change-over system be; ing a simplepentagonalprism Z, while the stationary system is an optical square,which, for effecting the required displacement of the pencils of rays,is cemented together out of two parts Z and Z with an interposed rhombicprism Z Fig. 16 shows a side elevation of this system 1 ,1 Z. In

.. this case as well for passing to the correctin position a rotation ofthe pentagonal PIISII]. I through 180 the plane of measurement isnecessary.

I claim:

1. In a telemeter twotelescope systems with their objective axes lyingin the baseline of the instrument, two reflecting systems, each of whichbeing adapted to deflectthe rays entering it by 90, one of thesereflecting systems being fixed in front of one of the said telescopesystems, and means for fitting the other reflecting system alternatelyin front of the other telescope and, rotated by 180 in the plane ofmeasurement, in front of the said reflecting system in such a positionthat in this case the two telescope systems are directed to points lyingin the same plane perpendicular to. the plane of measurement.

2. In a telemeter two telescope systems with their objective axes lyingin the baseline of the instrument, two reflecting systems, each of whichbeing adapted to defleet the rays entering it by 90, at least one ofthese reflecting systems being. a threequarter Porro system, one ofthese reflecting systems being fixed in front ofone of the saidtelescope systems, and means for fitting the other reflecting systemalternate ly in front of the other telescope and, rotated by 180 in theplane of measurement, in front of the said reflecting system in such aposition that in this case the two telescope systems are directed topoints lying in the same plane perpendicular to the plane ofmeasurement.

OTTO EPPENSTEIN.

